i) Field of the Invention
The present invention relates to a lithium ion nonaqueous electrolyte battery, a lithium titanium composite oxide, and a battery pack.
ii) Related Art
A nonaqueous electrolyte battery which performs charge and discharge actions as a result of transfer of lithium ions between a negative electrode and a positive electrode has been actively researched and developed as a high-energy density battery.
A nonaqueous electrolyte battery using a lithium-transition metal composite oxide as a positive electrode active material and using a carbonaceous substance as a negative electrode active material has currently been commercialized. In relation to the lithium-transition metal composite oxide, Co, Mn, Ni, and the like, is usually used as transition metal.
Attention has been recently paid to a lithium titanium composite oxide exhibiting a higher Li absorption-release potential than that of a carbonaceous substance. The lithium titanium composite oxide has advantages that lithium metal is not deposited in principle at the lithium absorption-release potential and that the composite oxide is superior in terms of quick recharge and low-temperature performance.
Of the lithium titanium composite oxides, spinel lithium titanate [a composition formula Li4+xTi5O12 (0≦×≦3)] has especially gained attention on the ground that a volumetric change developing during charge and recharge periods is small and that superior reversibility is achieved. However, the theoretical capacity of spinel lithium titanate is 175 mAh/g, and there are limitations to an increase in capacity.
In addition to lithium titanate having a spinel crystalline structure, a lithium titanate compound having a ramsdellite crystalline structure has also been known (JP-A-10-247496 (KOKAI)). The theoretical capacity of ramsdellite lithium titanate is 235 mAh/g and is greater than that of spinel lithium titanate. Therefore, an increase in capacity can be expected theoretically.